I'd just like to say, that when I first saw this entry I knew who it was about. Bree you're a really good friend. I'm pretty sure she was in a dark place at the time. But hopefully she's better now.
I will not give up on her,ever. I have talked to my mom about it and she told me basically the same thing you are all telling me.
We both used to cut and burn ourselves and stopped, and we call/text the other when either of us are close to hurting ourselves. I also know that my trying to help her will cause her parents to get angry, but it will be worth it if I can prevent her from doing something terrible.
Tell someone. I know you may get in shit or whatever. But if you don't. She won't get help. Might end up cutting herself or even burning. And everything will get worse. Tell someone. Get her help.
The best advice I can give you, would be to talk to someone that you trust (an adult such as your parents, a school counselor etc) and let them know what's going on. If she's serious about suicide, then she needs help, and this is a situation you might not be able to give her the right kind of help she needs.